The present invention relates to an expanding-fluid type thermometer. More particularly this invention relates to a thermometer having a dyed silicone fluid as a visible expanding fluid.
Expanding-fluid type thermometers of the capillary-tube type are ancient and the variety of expanding fluids that have been used therein as the temperature-responsive means is broad. However, most expanding fluids suffer from one or more deficiencies that limits their use in a thermometer.
For example, a narrow liquid range is displayed by most fluids and therefore limits their use at high and/or low temperature. Alcohol, although useful at low temperature, is an example of a fluid that is not useful at high temperature because it boils. Mercury, although useful at high temperature, is an example of a fluid that is not useful at very low temperatures because it freezes.
Another deficiency of mercury is its toxicity. A broken mercury-type thermometer can release mercury into the environment, necessitating a clean-up of the released mercury. This deficiency is particularly important in the processing of food wherein the released mercury might enter the food being processed and/or the food-processing equipment.
Silicone fluids are well known to have a wide liquid range, good stability at high temperature and a very low toxicity and would appear to be ideally suited as a temperature-responsive means in an expanding-fluid type thermometer. However, silicone fluids are colorless and are nearly impossible to see in a capillary tube, thus making it difficult for the human eye to locate the meniscus of the capillary fluid. Furthermore, most dyes have limited solubility in silicone fluids and do not contribute sufficient color to a capillary column of silicone fluid.